Individuals with aggression regulation disorders tend to attribute hostility to others in socially ambiguous situations. Previous research suggests that this “hostile attribution bias” is a powerful cause of aggression. Facial expressions form important cues in the appreciation of others’ intentions. Furthermore, accurate processing of facial expressions is fundamental to normal socialization. However, research on interpretation biases in facial affect is limited. It is asserted that a hostile interpretation bias (HIB) is likely to be displayed by individuals with an antisocial (ASPD) and borderline personality disorder (BPD) and probably also with an intermittent explosive disorder (IED). However, there is little knowledge to what extent this bias is displayed by each of these patient groups. The present study investigated whether a HIB regarding emotional facial expressions was displayed by forensic psychiatric outpatients (FPOs) and whether it was associated with ASPD and BPD in general or, more specifically, with a disposition to react with pathological aggression. Participants of five different groups were recruited: FPOs with ASPD, BPD, or IED, non‐forensic patients with BPD (nFPOs‐BPD), and healthy, non‐aggressive controls (HCs). Results suggest that solely FPOs with ASPD, BPD, or IED exhibit a HIB regarding emotional facial expressions. Moreover, this bias was associated with type and severity of aggression, trait aggression, and cognitive distortions. The results suggest that a HIB regarding facial expressions is an important characteristic of pathological aggressive behavior. Interventions that modify the HIB might help to reduce the recurrence of aggression. Aggr. Behav. 43:386–397, 2017. © 2017 Wiley Periodicals, Inc.